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Easy Home Control Via Web Chat 


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build, hack, tweak, share, discover, J 

Easy Home Control Via Web 


Written By: Lee von Kraus 



Soldering iron (1) 

RadioShack part #64-2802 or #276- 
1570. Wrapping wire around component 
leads is less permanent than soldering, 
but it's OK for prototyping. 

Computers (2) 

One for home, and one for the remote 

location. It's helpful if one has a 


Webcam (1) 

that you can move and point (i. e. not 

built into the screen) 

Wrapping wire (1) 
RadioShack #278-503 

RadioShack #278-503(1) 
RadioShack #276- 1657 

Transistors (1) 
2N222 A/PA/ 

Breadboard (1) 
RadioShack #276-003 

Devices (1) 

that you want to control remotely 

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Easy Home Control Via Web Chat 

Power supplies (1) 

with voltages that match your devices. 
You probably have some spare wall- 
warts from appliances you don't use 



but recommended, large enough to hold 

your computer screen 

Dark surface (1) 

Flashlight (1) 


If you have pets or children that you need to feed or check on via the internet, here's a 
cheap and easy way to control motors, lights, and other devices at home from another 
computer online, like the one at work. You can set this system up in minutes and it requires 
no programming. All you need is a webcam, a flashlight, a standard computer running free 
software, and about $15 worth of analog electronics you can buy at RadioShack. 

The system works through a Yahoo Messenger video chat connection between your home 
computer and any remote computer. But instead of showing people talking, the video stream 
conveys simple control information that you "encode" using a flashlight on a plain dark 

With my setup, for example, shining a light in the upper left corner of the image powers a 
dog food "allower" that uncovers a dog dish, and shining it in the lower right sounds a buzzer 
to signal dinnertime. 

On the home computer, the video chat window runs full-screen, and cheap photosensors 
taped onto the screen's surface detect the changes in brightness when the flashlight spot 
image hits their locations. Each sensor then switches its device at home via a transistor or 
relay. Voila! 

By using the screen itself as a port, you bypass having to unpack USB or some other 
protocol, and you can add additional actuators by simply taping sensors to different parts of 

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Easy Home Control Via Web Chat 
the screen. 

This setup also keeps your home computer more secure than remote desktop access 
software such as VNC, unless Yahoo Messenger has some super-secret way of controlling 
your whole computer, which is unlikely. 

Photo resistor 


2N222 transistor 
or relay. 


(repeat circuit 


Full-screen video feed from work 
computer sent via Yahoo Messenger. 

Install Yahoo Messenger ( ) on both your home and remote 
computers. Make 2 accounts under 2 matching names, one ending in "home" and the other 
ending in "work" (you'll need 2 email addresses for this; get free ones from Gmail or 
Hotmail or something). 

Separately log into each account from their respective machines, add them as friends for 
each other, and configure their Webcam preferences to "Allow everyone to view my 
webcam" and their Super Webcam preferences to "Start Super Webcam mode 

For each device you want to control, solder or wire-wrap a long length of wire to each of 
the 2 leads of a photoresistor. Set up a power circuit for each device on a breadboard, 
following the schematic. All of the power supplies should be plugged into a surge protector, 
like a power strip with a circuit breaker. 

You may need to insert an additional transistor/relay for higher-powered devices. 

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Easy Home Control Via Web Chat 

Then test whether the switching works for each device by covering and uncovering the 
photoresistors with your hand. 

Use electrical tape to tape the photo-resistors sensor-side down on the computer screen, 
spaced apart. Adjust the screen brightness to a level such that the devices switch off 
when the screen is black. 

With some circuits, I found that I had to put a piece of paper between the photoresistor and 
the screen to reduce the light. I recommend also putting the computer screen in a box to 
exclude non-screen light that could interfere with the sensor readings. 

Set up your devices however they're going to work. It helps if your home computer has a 
webcam pointed at the devices, so you can remotely watch what's happening. 

At your work computer, connect a webcam and set it up so that it looks at a dark, flat 
surface. I used a PVC stand that I'd already made for the camera and pointed it down onto 
a black T-shirt. 

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Easy Home Control Via Web Chat 

• On your work computer, run Yahoo 
Messenger. Next to your home 
username, select View My 
Webcam to open a webcam feed, 
then leave it running. 

• On your home computer, click to 
view your work video feed. Change 
the window size so it fills your 
home computer's screen, or at 
least covers the area around all the 

• Back at work, shine a flashlight into 
the camera's field of view at 
different locations to activate the 
devices controlled by your home 
computer screen. 

Test your system for a full day before you put it to use while you're away. Because it's 
based on analog sensors taped to a screen, there are little ways in which the "real world" 
will interfere with it. For instance, the photoresistors might fall off, or be triggered by 
changes in daylight coming through the windows. 

If you want to control home devices wirelessly, I suggest an inexpensive, low-power 
infrared remote system like the Tiny-IR-ll from Reynolds Electronics ( ). 
Just replace the switches in the Tiny-IR-ll encoder chip schematic with your photo-resistor 
circuits' transistors, and use a decoder chip for each device. 

Note that the system's range isn't great, and it uses infrared, like a TV remote, so 
all the devices should be in the same room as the transmitter. 

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Easy Home Control Via Web Chat 

• With an IR remote system, it would also be good to dedicate an additional photoresistor 
circuit to a relay that all the other device circuits traverse. That way, you would have a "kill 
switch" that can shut the whole thing down if it starts acting wacky. 

• For more complex control, you can connect the sensor signals to a microcontroller. For 
my home system, I connected the transistor outputs to a PIC microcontroller and H-bridge 
motor controller IC that run a simple motorized dog food allower and a piezo buzzer. 

• Both could be connected directly, as shown in the diagram in Step 1 , but I put a PIC in the 
loop to allow more complex outputs in the future. 

• I hope that this system helps people and also helps make some pets happier when they're 
at home alone. 

This project first appeared in MAKE Volume 22 . page 57. 

This document was last generated on 201 2-1 1 -01 1 0:49:1 1 AM. 

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